Nanofabrication of top-gated carbon nanotube-based transistors: Probing electron-electron interactions in one-dimensiona
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Z.Z. Bandic´ Hitachi San Jose Research Center, San Jose, California 95120
D. Goldhaber-Gordon Department of Physics, Stanford University, Stanford, California 94305 (Received 31 March 2006; accepted 8 August 2006)
Carbon nanotubes are interesting for studying the remarkable electronic properties of one-dimensional (1D) quantum systems. Electron flow in such systems is not described by Fermi liquid theory—restricted dimensionality leads to the appearance of collective excitations—or Luttinger liquid behavior. Previous studies have probed Luttinger liquid behavior by tunneling into or between one-dimensional systems. We propose to extend these studies by using narrow top gates to introduce tunable tunnel barriers within nanotubes. We report on the scalable fabrication of carbon nanotube-based transistors with nanowire top gates. We have used electron-beam lithography (EBL) to create single-walled carbon nanotube (SWNT) transistors with source-drain spacings down to 200 nm and with sub-30 nm metal top gates for creating tunable tunnel barriers. The top metal gate is isolated from the nanotube by a thin aluminum oxide layer deposited by atomic layer deposition. We fabricated chips with 100 devices using multiple electron-beam lithography alignment steps and achieved overall placement better than 30 nm. The details of top-gated SWNT transistor fabrication are presented, and initial transport measurements on fabricated devices are discussed. I. INTRODUCTION
Carbon nanotubes have attracted significant interest for studying electronic properties of one-dimensional (1D) electron systems.1–5 Electron flow in three dimensional systems has been successfully described by Landau Fermi liquid theory,6 in which there exists a oneto-one correspondence between non-interacting and interacting electron states (quasiparticle excitations). In these systems, the important electron scattering processes occur around the Fermi level, significantly simplifying quantitative analysis [Figs. 1(a) and 1(b)]. The approximations of Landau Fermi liquid theory are correct when the electron–electron relaxation time ee is much larger than both the relaxation times for scattering of electrons with phonons and impurities, e−ph and e−imp respectively.7 Essentially, quasiparticle excitations in higher dimensional systems behave as nearly free particles (i.e., the particles can “move past each other”). However, the Landau Fermi liquid theory description of many-body systems is not valid for interacting systems in 1D. The restricted dimensionality in 1D changes the nature of
electron–electron scattering so that only collective excitations exist in interacting systems [Fig. 1(c)]. The theoretical description of the interacting 1D quantum state, first developed by Tomonaga and Luttinger,8,9 involves plasmon-like excitations that behave as bosons.10–12 In such a Luttinger liquid, a highly correlated many-electron state emerges as a consequence of the reduced dimensionality and electron–electron interactions. This correlated state is characterized by a p
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